1. Field of the Invention
The present invention relates to a shank a rotatable and/or percussively driven working tool such as a drill bit, a chisel, or a core bit for working stone, concrete, or masonry
2. Description of the Prior Art
Usually, a rotary/percussion working tool such as, e.g., disclosed in German Publication DE39 41 646 A1, has a shank extending along the tool axis and having cylindrical guide surfaces, locking grooves, which are axially closed at their ends adjacent to the free end of the shank, and axially open entrained grooves. Radially displaceble locking members, which are provided in an associated chuck, engage in the locking grooves, limiting axial displacement of the working tool.
According to German Publication DE 196 04 283 A1, a shank can have three additional webs which extend up to the free end of the shank and circumferentially arranged between the grooves. The entrained surfaces, which are located radially inwardly with respect to the diameter of the cylindrical guide surfaces, necessitate, because of their small radial distance from the axis, application of high contact surface pressures for effecting torque transmission. As a result of the application of high contact surface pressures, they rapidly wear off. Because these grooves are formed by machining them in a previously round shank, the impact or blow transmitting cross-section, which is available in the shank, is reduced. As a result, disturbing reverberations, which take place, weaken the pulse transmission.
According to German Publication DE 34 13 432 A1, a shank has three circumferentially, uniformly distributed grooves axially closed at their opposite ends. The grooves are formed by a non-cutting, embossing process in a round blank, with radial portions of increased height provided on tangential nut edges. The increased height portions permit to increase the rotation-transmitting outer diameter of the shank, which defines guide surfaces of shanks of different diameters and receivable in a special three jaw chuck. Because the guide surfaces are formed by increased height portions on the tangential groove edge, this shank is unsuitable for transmitting of high torques that cause an extensive wear.
German Utility Model DE 84 33 275 U1 discloses a shank having three circumferentially uniformly distributed grooves closed at their respective opposite axial ends and formed by a non-cutting, embossing process in a round blank. The grooves, which are formed as recesses, are associated with respective radial protrusions. In the shank of the utility model DE 84 33 275 U1, the central recess angle is smaller than the central protrusion angle. With a suitable deformation tool and taking into consideration a longitudinal expansion of the blank during the deformation process, a uniform displacement of material radially outwardly over the cross-sectional area is achieved. Thereby, a rotation-transmitting outer diameter of the shank correspondingly increases. In case when some longitudinal expansion is allowed, the outer diameter corresponds to that of the blank. With wide radial protrusions, the deformable material is not optimally used for increasing the torque transmission.
Accordingly, an object of the present invention is to provide a shank for a rotatable and/or percussively driven working tool capable of transmitting high torques, without being subjected to a noticeable wear, and having good pulse characteristics.